Why do the wood-elves capture and imprison the dwarves?
The Elven-king imprisons the dwarves because he believes them to be trespassing in his kingdom and that they tried to attack his people.
The Elves felt they were being attacked and responded in kind. Since Thorin refused to tell them why he was in their realm, for fear they would want some of the treasure (he coveted the Arkenstone and feared others would try to take it), they decided to imprison him just to be safe. The Elves distrusted the Dwarves, and they had, for many years, been seen as beggars.
At first the dwarves were captured because the Elf King had thought that the company was attacking the feasting elves. Then, when the king questioned them, they refused to answer, and finally Balin asked why they were being held prisoner. The elf king answered, "It is a crime to wander in my realm without leave... After all the disturbance you have made i have a right to know what brings you here, and if you…
Smaller than a regular star. Please note that there are different types of stars called "dwarf star", with quite different sizes: red dwarves, white dwarves, brown dwarves, white dwarves, and the hypothetical black dwarves (which are not expected to currently exist). White dwarves (and black dwarves) are the smallest of these, with a size about as big as our Moon.
It occurs on several occasions. In the mountain being chased by the goblins, he falls and is knocked out and the goblins overlook him. In Mirkwood, the spiders capture them and Bilbo has to rescue them. Again, the Elves capture the party and Bilbo escapes, partially due to his small size and his magic ring.
In The Hobbit the thirteen dwarves are imprisioned by the Wood Elves of Mirkwood because Dwarves and Elves have never been on good terms, consiquently the Elves are suspisious that the dwarves were plotting some foul plan. The Elves were very ticked that the dwarves kept interupting their festivites in Mirkwood. When the dwarves are questioned about what they are doing in Mirkwood, they refuse to answer, making Thranduil (the Elvenking of Mirkwood) extremely suspious…